The coalition government has pledged that the BBC's editorial independence will not be harmed by giving the National Audit Office carte blanche to investigate the corporation's books, with contentious areas such star salaries set to remain confidential under the new deal.

Don Foster, the Liberal Democrat culture spokesman, speaking at the party's conference today, confirmed that the NAO would be able to get access to "any information it needs to carry out its studies", including confidential BBC contracts with third parties including top talent.

"The coalition wants this focus on value for money to go further [and] to help achieve this we said we would seek ways of giving the National Audit Office full access to the BBC's accounts so that, working with the BBC Trust, we could ensure even greater transparency and value for money," said Foster. "It [the NAO] will see BBC management information and confidential BBC contracts with third parties. In all, it will be able to get a hold of any information it needs to carry out its studies. But it will happen in a way that always ensures the editorial independence of the Beeb."

The culture secretary, Jeremy Hunt, agreed the NAO access arrangement with the BBC Trust, the Department for Culture, Media and Sport confirmed. The main points are that the NAO:

• will have routine access to BBC management information;

• will have the right of access to any information it needs to identify and carry out its studies;

• will have access to confidential BBC contracts with third parties;

• will not question the BBC's editorial policy.

The BBC Trust will be "consulted" on any intended programme of NAO investigations so that the corporation's governing body "can inform the process and conduct additional studies where it feels appropriate".

This arrangement will not "undermine" the BBC Trust, which will still be responsible for "rigorous stewardship of public money and for commissioning value for money investigations into specific areas of BBC activity", the government said.

The BBC Trust will also be allowed to commission its own value-for-money reports from other advisers.

Part of the agreement will enshrine the principle that the NAO "will not question" the BBC's editorial policy, in a move clearly designed to protect the corporation's independence from political interference.

A BBC Trust spokeswoman said: "We support a move to allow the NAO to choose which areas of BBC operations it will review on an annual basis. In our view, this does not threaten the BBC's independence from government or parliament, provided that the NAO continues to report to the trust and does not question editorial decision-making. Subject to further discussion between the trust and the DCMS [Department for Culture, Media and Sport], we are confident that this change can be made through amendments to the BBC agreement within the terms of the existing charter."

"The BBC is the best public service broadcaster in the world and, thanks largely to the peerless World Service, the envy of the world," he said. "Liberal Democrats have always argued for a healthy, diverse media with a strong, independent BBC at its heart. Of course, however strong our support for the BBC, we can't allow it to waste licence fee payers' money. We want it to provide value for money and focus on playing its part in investing in high quality UK content."